Tin-coated object



Patented a. 17, 1939 UNITED STATES PATENT OFFICE N atio Michigan pal-Standard Company, a corporation of No Drawing. Application December 4, 1937, Serial No. 178,176

3 Claims. -(Cl. ill-68.2)

This invention relates to ferrous base articles coated with a hot coating of a physically protecting metal, and with an outer coating of electroplated tin.

In the protection of ferrous base materialsagainst corrosion, it is quite customary to coat ferrous base objects with lead or tin or coatings v antimony alloys or lead-tin alloys, is remarkably improved by applying thereto a layer of electroplated tin.

The addition of an electroplated coat of tin is particularly valuable in the protection of the metal against acid treatment, for example, such acidic treatment as prescribed by the United States Army tinned coating test.

As an example of the invention, a ferrous base material, which is usually a sheet or wire, but is not limited tosuch objects, is immersed in the molten metal and is then wiped with asbestos. The wiping produces a rather smooth coating substantially uniformly over the entire article, the coating having a thickness ,of approximately between 1/5,000th and 1/20,000th of an inch.

The freshly treated material is then electroplated with a uniform layer of tin to form a coating having a thickness of 1/ 10,000th to 1/5,000th of an inch. The material is plated while immersed in either an alkaline or an acid tin solution. The sheet or wire or other object is so treated in the plating operation as to form a uni- I form layer coextensive with the undercoating, and both 'coatings cover entirely the surface to be protected.

It is important that the lower coating be undisturbed and undistorted in order that it present a uniform basis forthe uniformly applied outer coating.

A lower coat is preferably a lead-antimony alloy containing from 2 to 30% of antimony and preferably about 5% antimony and lead. Initial coatings of hot tin, or of alloys of lead and tin may likewise be employed. Antimony may be employed with the tin as well as with the 5 lead. I

The reason for the unexpected improvement by the addition of the electroplated coat is not understood, particularly in view of the fact that all of the metals listed are electropositive with re- 10 spect to hydrogen or iron-that is, they are less active and protect by physical means only, rather than electrolytically.

A ferrous base coated with lead or tin and then with hot tin in this manner produces a product 15 which shows remarkable resistance to successive dipping into hydrochloric acid and potassium ferrocyanide in accordance with the U. S. Army tinned coating test.

The foregoing detailed description has been 20 given for clearness of understanding only, and no unnecessary limitations should be understood therefrom, but the appended claims should be 'to 1/5,000th or an inch.

3. The method of protecting a ferrous base object against corrosion which comprises immersing the object in a molten metallic bath predominantly composed of lead and antimony, and then 40 electroplating over the entire coated surface of the object a coating of tin having a thickness of the order of 1 /10,000th to 1/.5,000th of an inch.

IEGIN OARLE'ION DOMM. 

